Patio inquiry

I laid this patio, 2200 sq ft, of irr Penn Blue stone. It is on 5" 411 (compacted gravel w/ dust) and 5" of re-inforced concrete. The mortar is 1/2" - 1 1/2" below stones and about 1/2" - 3/4" joints. After about 2 weeks, we are starting to see some small cracks along the seams of some of the joints. I am thinking that it may be due to the extreme heat we have been having causing the mortar to cure/dry too quickly. I am not having any of the issues with the walls though...

I have seen this happen from mortar drying to quick. I prefer type s at a 3 to 1 mix. Also adding a little more lime when it is really hot will help slow the cure a little by helping retain moisture longer.

The only way I have ever repaired a hair-line crack before was with an almost liquid mortar mixture and rub it into the crack. With joint cracks, usually bigger ones, I would grind out some of the mortar first so I could put in a healthy amount of mortar to minimize its chances of popping.